726 apparently healthy subjects from the BLSA underwent serial maximal exercise treadmill testing since 1969, the risk of future cardiac events was compared in those whose initial test was positive (Group I) versus those converting from negative to positive (Group II) over a 6.4 year mean followup. Group I Group II p n 86 92 age 64 63 NS men (%) 63 87 .01 events 17 17 NS events/100 persons-yrs 2.8 3.2 NS Combining groups I and II, the incidence of future events was 3.5 times as great in the 176 subjects with positive exercise ECG's as in the 548 individuals whose tests were consistently negative. Thus in asymptomatic subjects, serial conversion from a negative to a positive exercise ECG is of no greater predictive value for a future coronary event than an initially positive response. To determine the effect of silent myocardial ischemia on maximal exercise performance in totally asymptomatic subjects, we compared exercise duration, maximal heart rate (MHR), systolic blood pressure, and rate-pressure product at maximal treadmill workload in 21 asymptomatic BLSA volunteers (ages 57-81 yrs) who has ischemic ECG and thallium scan responses to maximal treadmill exercise with results in age-matched nonischemic BLSA controls. No differences in any of these parameters were noted between the groups.